| 摘要 |
758,240. Electron microscopes. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET. Oct. 26, 1954 [Nov. 4, 1953], No. 30817/54. Class 39 (1). The fluorescent coating of the viewing screen of an electron microscope is earthed via a current measuring device and provides a measure of the exposure necessary for a photographic film or plate. If the conductivity of the fluorescent layer is low, the glass support is first coated with a thin transparent conducting layer, e.g. of gold. The current from the screen is passed to a high resistance 2 and the voltage across it is amplified in the cathode follower valve 3, 9 and recorded on measuring instrument 11. In an alternative method, the time of exposure is controlled by providing an R.C. circuit connected to point 16 between resistances 61, 6<SP>11</SP> which can be connected to the grid of the valve 3. When switch 15 is operated, the grid receives the potential of point 16 which gives full deflection at instrument 11, and as the condenser 14 charges the deflection falls slowly to zero. By suitable design of the condenser and the resistances, the time taken to fall to the original deflection given by the microscope is the true exposure time and the microscope is switched on and off at these points. |
